ABSTRACT:
Fault reactivation resulting from fluid production or injection in porous reservoirs may be accompanied by seismic activity, ground deformation, well damage and the creation of fluid leakage paths. To ensure acceptable reservoir performance in hydrocarbon production or geological storage projects, it is critical to assess the reactivation tendencies of existing faults and fractures. In this paper a poroelastic, semianalytical model for predicting induced stress changes is summarized, and a methodology to assess fault reactivation tendency based on the Coulomb Failure Stress Change (?CFS) concept is presented. Critical parameters presented in the paper are cast in dimensionless form, to facilitate the use of this methodology to a broad range of problems. The Lacq gas field in France is used as a demonstration case study. The induced stress changes predicted for this domed-shaped reservoir show some differences with the results predicted by simpler models founded on the assumption of a planar reservoir geometry. Predicted fault reactivation tendencies show a strong correlation to recorded seismic event locations.
1 INTRODUCTION
During fluid production from hydrocarbon reservoirs, and fluid injection for enhanced oil recovery, waste disposal or greenhouse gas storage, stress changes are induced within and surrounding the reservoir. To ensure that production or injection can be maintained in a safe and effective manner, it is critical to assess the effect of these stress changes on the hydraulic integrity of the rocks that bound the reservoir. For example, if shear or tensile failure surfaces are induced, or if existing faults or fractures are reactivated, these features are likely to serve as fluid leakage paths. Furthermore, wellbores within or overlying the reservoir might be sheared and damaged, compromising their hydraulic integrity, and surface structures might be damaged due to subsidence. In extreme cases, earthquakes may be induced, causing damage to operations equipment and civil structures.
